1. Field of the Invention
The invention relates to a driving circuit for a brushless direct-current motor, particularly a fan motor, with a rotor position transmitter, and a control circuit which, depending upon the output signals of the rotor position transmitter determines the commutation phases and within the latter prepares output signals for the individual motor windings, the amplitude and/or duration of which are controlled or regulated depending upon a desired value or a guiding value, as well as a supply part to supply the control circuit including the rotor position transmitter with direct current from an alternating current supply.
2. Discussion of the Related Art
Already known from PCT Publication No. WO 87/02528 is a control circuit for brushless direct-current motors which, in the form of an integrated circuit, contains all the circuitry for the direct control of the motor windings, and is presented with a minimum of external constructional elements, namely a Hall-effect sensor as a rotor position transmitter and a single capacitor as a time function element in a pulse wave shape generator of the control circuit.
With this known control circuit it is possible to control or to regulate the power supplied to the direct-current motor depending on a desired value or a guiding value, so that it can be adapted to requirements. For example, it is possible, when using the brushless direct-current motor as a fan motor, to control the cooling performance of the fan depending upon the heat development of an electronic apparatus, i.e., when heat development is low the fan rotates slowly and produces little noise, whereas, for a higher development of heat, the fan runs faster and supplies a greater amount of cold air. This known control circuit with end steps is supplied by means of a low operational direct-current voltage of, e.g., 12 V., which, normally, is taken from the anyway available supply part of the electronic apparatus.
However, there are limits to the performance of such a brushless direct-current motor including control circuit and end steps, which limits are determined in particular by the maximum permissible loss performance in an integrated circuit. In addition, the amount of direct current which can be supplied from the supply part of an available electronic apparatus is also limited. Accordingly, normally, the larger fans are supplied direct from the alternating current supply so as not to overload the supply part of the electronic apparatus. Such a fan is then, however, not regulable normally in terms of its performance, so that, also in the case of necessary cold performance, the fan continues to rotate on full power with relatively high noise.